C++ 示例：定义参数

class Add2intsWithConstantFactory : public ScalarFunctionFactory
{
    // Return an instance of Add2ints to perform the actual addition.
    virtual ScalarFunction *createScalarFunction(ServerInterface &interface)
    {
        // Calls the vt_createFuncObj to create the new Add2ints class instance.
        return vt_createFuncObj(interface.allocator, Add2intsWithConstant);
    }
    // Report the argument and return types to Vertica.
    virtual void getPrototype(ServerInterface &interface,
                              ColumnTypes &argTypes,
                              ColumnTypes &returnType)
    {
        // Takes two ints as inputs, so add ints to the argTypes object.
        argTypes.addInt();
        argTypes.addInt();
        // Returns a single int.
        returnType.addInt();
    }
    // Defines the parameters for this UDSF. Works similarly to defining arguments and return types.
    virtual void getParameterType(ServerInterface &srvInterface,
                                  SizedColumnTypes &parameterTypes)
    {
        // One int parameter named constant.
        parameterTypes.addInt("constant");
    }
};
RegisterFactory(Add2intsWithConstantFactory);

/**
 * A UDSF that adds two numbers together with a constant value.
 *
 */
class Add2intsWithConstant : public ScalarFunction
{
public:
    // Processes a block of data sent by Vertica.
    virtual void processBlock(ServerInterface &srvInterface,
                              BlockReader &arg_reader,
                              BlockWriter &res_writer)
    {
        try
            {
                // The default value for the constant parameter is 0.
                vint constant = 0;

                // Get the parameter reader from the ServerInterface to see if there are supplied parameters.
                ParamReader paramReader = srvInterface.getParamReader();
                // See if the user supplied the constant parameter.
                if (paramReader.containsParameter("constant"))
                    // There is a parameter, so get its value.
                    constant = paramReader.getIntRef("constant");
                // While we have input to process:
                do
                    {
                        // Read the two integer input parameters by calling the BlockReader.getIntRef class function.
                        const vint a = arg_reader.getIntRef(0);
                        const vint b = arg_reader.getIntRef(1);
                        // Add arguments plus constant.
                        res_writer.setInt(a+b+constant);
                        // Finish writing the row, and advance to the next output row.
                        res_writer.next();
                        // Continue looping until there are no more input rows.
                    }
                while (arg_reader.next());
            }
        catch (exception& e)
            {
                // Standard exception. Quit.
                vt_report_error(0, "Exception while processing partition: %s",
                    e.what());
            }
    }
};